1. Field
This patent specification relates to an information record and playback apparatus in use for information recording media such as optical disks, magneto-optical disks and other similar media, and more particularly, to a demodulation circuit in such apparatus configured to carry out address demodulation.
2. Discussion of the Background
In data recording media such as optical disks, for example, it has been known to provide data prefabricated on the disk and include address information utilized for specifying the position for recording data, and information such as synchronization signals and wobbling signals for controlling the disk rotation, and other similar data.
As optical recording media capable of additionally writing (or recording) information data on the basis of these pre-data, also known previously are CD-recordable (CD-R) disks which have the approximately same storage capacity as compact disks (CDs).
The pre-data are in general prepared by forming in advance recording tracks such as grooves and lands for recording information data, in which the pre-data to be recorded are first frequency modulated (FM) to obtains FM signals. Subsequently, the pre-data to be recorded are incorporated into the disk by forming recording tracks to have a wobbling surface with the wobbling frequency corresponding to the FM signal frequency.
In order to additionally record information data into the CD-R disks, a playback apparatus detects wobbling signals from the wobbling pattern on the disk to obtain a wobbling frequency, then extracts standard clock signals for controlling the disk rotation on the basis of the wobbling frequency. In addition, the apparatus generates necessary drive signals for controlling the rotation of a spindle motor in use for the CD-R disk rotation, then generates recording clock signals including timing signals in synchronous with the CD-R disk rotation.
Also in the CD-R disks, address information on the disks needed for information data recording is obtained by first playing back the pre-data during the data recording and subsequently detecting the position to record on the basis of the pre-data, to thereby be able to achieve the recording.
High density recording media have also been put into practical use recently, such as digital video disks or digital versatile disks (DVDs), which has an increased storage capacity over the previous CDs.
Among the higher density storage media exemplified by the DVDs, information data tracks (e.g., grooved tracks) are formed, having the aforementioned wobbling surface on the basis of the frequency corresponding to standard clock signals. This method is used in optical recording media such as write once type DVD recordable (DVD-R) and DVD Rewritable (DVD+RW) media.
Regarding error correction for the pre-data recorded into the DVD-R and DVD+RW disks, it is necessary to add a plurality of data to be utilized in the error correction, since the position and pattern of an error have to be computed. The error correction data are typically exemplified by the Reed-Solomon code which has been in use for not only DVD disks but also CDs and digital audio tapes (DATs).
As the data to be added for the error correction using the Reed-Solomon code, parity words consisting of at least 2t words are necessary for correcting an error of t words.
For example, for land prepit data (which is hereinafter referred to as ‘LPP’), a parity word consisting of three words is added to an address information data of three words, and one one-word error in the address information can be corrected. In contrast, for the case of address data in pre-groove (which is hereinafter referred to as ‘ADIP’), a five-words parity word is added to an eight-words address multiplex (MUX) information data, and one two-words error in the address MUX information can be corrected.
As described above, in error correction steps for the address data played back from the DVD type disks, there have previously persisted drawbacks such as low efficiency in the error correction, for example, in which the number of words which is successfully corrected is relatively small compared with the number of added parity words.